August 16, 2012

Oetzi the Neandertal champion

John Hawks reports that Oetzi, the Tyrolean Iceman appears to be much more "Neandertal" than any modern person. This is a very intriguing finding, which would have monumental implications about our understanding of our past.

Furthermore, he speculates that:

Paleogenetic evidence from Neandertals, the Neolithic and other eras has the potential to transform our knowledge of human population dynamics. Previous work has established the level of contribution of Neandertals to living human populations. Here, I consider data from the Tyrolean Iceman. The genome of this Neolithic-era individual shows a substantially higher degree of Ne- andertal ancestry than living Europeans. This comparison suggests that early Upper Paleolithic Europeans may have mixed with Neandertals to a greater degree than other modern human populations. I also use this genome to evaluate the pattern of selection in post-Neolithic Europeans. In large part, the evidence of selection from living people’s genetic data is confirmed by this specimen, but in some cases selection may be disproved by the Iceman’s genotypes. Neolithic-living human comparisons provide information about migration and diffusion of genes into Europe. I compare these data to the situation within Neandertals, and the transition of Neandertals to Upper Paleolithic populations – three demographic transitions in Europe that generated strong genetic disequi- libria in successive populations.

In our twitter exchange he seems open to the possibility I suggested that Oetzi might have excess Neandertal admixture from the Near Eastern Neolithic. He says: "@dienekesp Not impossible if there were relict Neandertals in West Asia. OTOH, UP morphology is consistent with > Neandertal."

Indeed, most of the argument for Neandertal admixture has focused on Neandertal morphological traits in UP Europeans. But, West Asia has been proposed as a site for modern human-Neandertal mixing, and a number of West Asian Neandertals appear to share modern traits.

There is a way to test whether the excess Neandertal admixture in Oetzi is due to his Mesolithic European or Neolithic Near Eastern component.

Make a map of sites where Oetzi has a signal of Neandertal admixture. Then, use a tool, such as my weac2 calculator which contrasts Europe (Atlantic_Baltic component) with the Near East (Near_East component). It is expected that a signal of Upper Paleolithic European ancestry will lurk in the Atlantic_Baltic component, while a signal of Near Eastern Neolithic ancestry will lurk in the Near_East component.

If the excess Neandertal occurs at regions of Oetzi's genome with an excess of Atlantic_Baltic then the UP European scenario is confirmed; otherwise the Neolithic Neandertal scenario is supported.

I have already made a map of Oetzi's genome. His overall admixture proportions using weac2 are:

1.05% Palaeoafrican

43.94% Atlantic_Baltic

0.00% Northeast_Asian

51.52% Near_East

1.54% Sub_Saharan

0.00% South_Asian

1.95% Southeast_Asian

and a fine scale map of his ancestry can be found here (NCBI 36 positions). I used a window of 100 SNPs, advanced by 10 SNPs. Admixture estimates within each window are obviously noisy, but if there is a pattern where Oetzi is more "Neandertal" in Atlantic_Baltic vs. Near_East regions, it ought to jump out.

So, anyone can look at regions where Oetzi matches Vindija and see whether Near_East or Atlantic_Baltic will carry the day in the Neandertal championships!

I am pretty sure the Neanderthal that is being used as a standard is part (maybe 25%) Homo sapiens. So the parts of Oetzi that we are calling neanderthal could really be ancient Tuscan or something similar(sapiens). We need a clearly neanderthal genome for these studies, not one that is shifted dramatically towards sapiens already.

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